Implantable coronary sinus lead with mapping capabilities

ABSTRACT

A cardiac lead is disclosed that includes a first lead body having opposed proximal and distal end portions and an interior lumen extending therethrough. The first lead body includes a sensor for measuring blood flow parameters to facilitate placement of the distal end portion thereof adjacent the coronary sinus. The first lead body has a distal electrode operatively associated with the distal end portion thereof and a proximal electrode operatively associated with the proximal end thereof. The second lead body has opposed proximal and distal end portions. A distal electrode is operatively associated with the distal end portion thereof and a proximal electrode operatively associated with the proximal end thereof. The second elongated lead body is dimensioned and configured for accommodation within the interior lumen of the first lead body.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The subject application is a continuation-in-part of U.S.application Ser. No. 09/912,796 filed Jul. 25, 2001 and acontinuation-in-part of U.S. application Ser. No. 10/000,647 filed Nov.11, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The subject invention is directed to an intravenous lead, andmore particularly, to an implantable cardiac lead and having mappingcapabilities to facilitate safe placement of the lead within thecoronary sinus.

[0004] 2. Background of the Related Art

[0005] Electrical therapeutic and diagnostic devices for the heart, suchas pacemakers and defibrillators, commonly employ leads for connectingan electrical pulse generator to excitable cardiac tissue, usuallywithin the right ventricle and/or right atrium. Pacing anddefibrillation leads commonly include one or more distal electrodes andoften have outwardly projecting tines near the distal tip or an activefixation screw to hold the electrode in contact with endocardial tissuein the right ventricle or atrium.

[0006] It has been found that cardiac stimulation can have a beneficialeffect in treating congestive heart failure. However, pacing therapy fortreating congestive heart failure often requires left ventricularstimulation, either alone or in conjunction with right ventricularstimulation and defibrillation. Left ventricular pacing presentlyrequires placement of an epicardial lead by way of a thoracotomy, whichis a high risk procedure performed under general anesthesia. To obviatethe need for a thoracotomy, left ventricular access leads have beendeveloped which are introduced through the coronary sinus and thenadvanced through the coronary veins so that the distal electrode of leadcan be positioned on the surface of the left ventricle near the apex ofthe heart.

[0007] The coronary veins of the heart are of a relatively smalldiameter. The lead extended therethrough must therefore, be of arelatively small diameter, as compared to leads used for rightventricular stimulation. Cardiac and respiratory motion as well as bloodflow can cause a lead to become dislodged. Accordingly, the lead mustinclude structure to anchor the electrode at a desired location.

[0008] It would be beneficial to provide a left ventricular pacing leadconfigured for advancement through the coronary sinus and into thecoronary vein, which has structure for anchoring the distal end of thelead at a desired site of stimulation, and which could be used incertain instances for defibrillation.

SUMMARY OF THE INVENTION

[0009] The subject invention is directed to a new and useful implantablecardiac lead adapted and configured for advancement through the coronarysinus and into the coronary vein that includes cooperating first (outer)and second (inner) elongated lead bodies. The first lead body hasopposed proximal and distal end portions, an interior lumen extendingtherethrough, at least one distal electrode operatively associated withthe distal end portion thereof and a proximal electrode operativelyassociated with the proximal end thereof. Preferably, the first leadbody includes sensor means that are operatively associated with thedistal end portion thereof for measuring blood flow parameters tofacilitate placement of the distal end portion of the first lead bodyadjacent the coronary sinus, and seal means for sealing the interiorlumen of the first lead body during insertion of the first lead bodythrough the coronary venous system.

[0010] The second (inner) lead body has opposed proximal and distal endportions, at least one distal electrode operatively associated with thedistal end portion thereof, a proximal electrode operatively associatedwith the proximal end thereof, and it is dimensioned and configured foraccommodation within the interior lumen of the first (outer) lead body.Preferably, the proximal end portion of the first lead body and theproximal end portion of the second lead body include means forconnecting the first lead body to the second lead body.

[0011] In accordance with the subject invention, the second lead bodyhas a length that is greater than the length of the first lead body.Preferably, the length of the first lead body is about between 50 and 80cm, and the length of the second lead body is about between 60 and 100cm. preferably, the outer diameter of the first lead body is aboutbetween 6 and 9 F, and the outer diameter of the second lead body isabout between 3 and 5 F.

[0012] A conductor extends through the first lead body to connect thedistal electrode and the proximal electrode, and a conductor extendsthrough the second lead body to connect the distal electrode and theproximal electrode. Additionally, the second lead body has an interiorlumen extending therethrough to accommodate a stylet. In one embodimentof the invention, the distal electrode of the first lead body is a ringelectrode spaced from the distal end of the lead body for pacing and/orsensing. Alternatively, the distal electrode of the first lead body is acoil electrode used for defibrillation, or as a ground electrode. In oneembodiment of the invention, the distal electrode of the second leadbody is a ring electrode that is spaced from the distal end of thesecond lead body for pacing and/or sensing. Alternatively, the distalelectrode of the second lead body is configured as tip electrode forpacing and/or sensing. The proximal electrode of the second lead body ispreferably defined as a pin connector.

[0013] The second or inner lead body preferably has fixation meansoperatively associated with the distal end portion thereof for anchoringthe lead within the coronary venous system. In addition, the first orouter lead body may have fixation means operatively associated with thedistal end portion thereof. In either case, the fixation means may bedefined by at least one radially expandable tine, by an expandable stentconfigured for movement between a retracted position and an expandedposition, or by a plurality of radially expandable arms configured formovement between a retracted position and an extended position.Furthermore, the fixation means may have a coating containing amedicament such as a steroid.

[0014] The subject invention is also directed to a new and useful methodof implanting a cardiac lead comprising the steps of passing anelongated outer lead body having an interior lumen through the venoussystem to a selected coronary vein, and extending an elongated innerlead body into the interior lumen of the outer lead body so that adistal end portion of the inner lead body extends from a distal endportion of the outer lead body.

[0015] The method further includes that steps of securing the inner andouter lead bodies to one another, and anchoring at least one of thedistal end portion of the inner lead body and the distal end portion ofthe outer lead body within the selected coronary vein. The step ofanchoring at least one of the distal end portion of the inner lead bodyand the distal end portion of the outer lead body within the selectedcoronary vein includes deploying an expandable stent operativelyassociated with at least one of the distal end portion of the inner leadbody and the distal end portion of the outer lead body, or deployingexpandable arms operatively associated with at least one of the distalend portion of the inner lead body and the distal end portion of theouter lead body.

[0016] These and other aspects of the subject invention and the methodof using the same will become more readily apparent to those havingordinary skill in the art from the following detailed description of theinvention taken in conjunction with the drawings described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] So that those having ordinary skill in the art to which thesubject invention pertains will more readily understand how to make anduse the cardiac lead of the subject invention, preferred embodimentsthereof will be described in detail hereinbelow with reference to thedrawings, wherein:

[0018]FIG. 1 is a perspective view of the two-part coronary sinus leadconstructed in accordance with a preferred embodiment of the subjectinvention, the distal end of which is in electrical contact with theleft ventricle of the heart through the great cardiac vein;

[0019]FIG. 2 is a perspective view of the two-part coronary sinus leadof the subject invention which includes an outer lead body having ananodic ring electrode associated with the distal end portion thereof,and an inner lead body configured for accommodation within the interiorlumen of the outer lead body and having a cathodic tip electrodeassociated with the distal end thereof;

[0020]FIG. 3a is a side-elevational view, in partial cross-section, ofthe distal end portion of the outer lead body, with the tapered distaltip thereof in an initially sealed condition to facilitate ease ofintra-vascular introduction;

[0021]FIG. 3b is a side elevational view, in partial cross-section, ofthe proximal end portion of the outer lead body;

[0022]FIG. 3c is a side elevational view, in partial cross-section, ofthe distal end portion of the inner lead body;

[0023]FIG. 3d is a side elevational view, in partial cross-section, ofthe proximal end portion of the inner lead body;

[0024]FIG. 4 is a side elevational view of the coronary sinus lead ofthe subject invention, with the proximal coupling of the inner lead bodypartially sectioned to illustrate the threaded engagement of theproximal end portions of the inner and outer lead bodies;

[0025]FIG. 5 is a side elevational view of another embodiment of thecoronary sinus lead of the subject invention configured for leftventricular pacing and sensing;

[0026]FIG. 6 is a side elevational view of another embodiment of thecoronary sinus lead of the subject invention configured for leftventricular pacing and sensing, and for right ventriculardefibrillation;

[0027]FIG. 7 is a side elevational view of another embodiment of thecoronary sinus lead of the subject invention configured for leftventricular pacing and sensing, and for right atrial pacing and sensing.

[0028]FIG. 8 illustrates the placement of the outer lead body of thecoronary sinus lead of FIG. 5, through the superior vena cava to aposition adjacent the auriculo-ventricular opening to the coronarysinus;

[0029]FIG. 9 illustrates the placement of the inner lead body throughthe interior lumen of the outer lead body and into the great cardiacvein of the heart through the coronary sinus;

[0030]FIGS. 10a and 10 b illustrate the retracted and extendedpositions, respectively, of an anchoring device associated with thedistal end portion of the inner lead body;

[0031]FIGS. 11a and 11 b illustrate the contracted and expandedpositions, respectively, of an expandable stent operatively associatedwith the distal end portion of the inner lead body;

[0032]FIGS. 12 and 13 illustrate additional embodiments of an expandablefixation device operatively associated with the distal end portion ofthe inner lead body;

[0033]FIG. 14 illustrates the deployment of the coronary sinus lead ofFIG. 6 which is configured for left ventricular pacing and sensing, inconjunction with a second lead configured for right ventricular pacingand sensing, as well as defibrillation;

[0034]FIG. 15 illustrates the deployment of the coronary sinus lead ofFIG. 7 which is configured for left ventricular and right atrial pacingand sensing, in conjunction with a second lead configured for rightventricular pacing and sensing, as well as defibrillation; and

[0035]FIG. 16 illustrates another embodiment of the coronary sinus leadof the subject invention wherein the a sensor is operatively associatedwith the distal end portion of the outer lead body for measuring bloodflow parameters to facilitate placement of the distal end portion of theouter lead body adjacent the opening to the coronary sinus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0036] Referring now to the drawings wherein like reference numeralsidentify similar structural features of the intravenous leads disclosedherein, there is illustrated in FIG. 1 a coronary sinus lead constructedin accordance with a preferred embodiment of the subject invention anddesignated generally by reference numeral 10. Coronary sinus lead 10 isadapted and configured for intravenous introduction to the great cardiacvein or branch vein through the coronary sinus so that an electrodeassociated with a distal end portion of the lead is in electricalcontact with the left ventricle of the heart. The proximal end of thelead is then operatively connected to an implanted therapeuticelectrical device such as a pacemaker. Once in contact, the distalelectrode of lead 10 may be employed for left ventricular pacing and/orsensing.

[0037] Referring to FIGS. 2 and 3a-3 b, coronary sinus lead 10 includesan outer lead body 12 and an inner lead body 14 configured for receptionand accommodation within an interior lumen of the outer lead body. Moreparticularly, the outer lead body 12 has opposed distal and proximal endportions 16 and 18, and an interior lumen 20 extending therethrough. Thedistal end portion 16 of lead body 12 is tapered to ease theintravascular placement thereof. A distal electrode 22 is operativelyassociated with the distal end portion 16 and a proximal electrode 24 isoperatively associated with the proximal end portion 18. The distalelectrode 22 is in the form of a ring electrode, as is the proximalelectrode 24. However, other types of electrode configurations can beemployed for purposes other than sensing and/or pacing as will bedescribed in more detail hereinbelow. The proximal and distal electrodes22, 24 of the outer lead body 12 are electrically connected to oneanother by a conductor such as a monofilliar or multifilliar coil 23,and they serve as the anode for coronary sinus lead 10. The proximal endportion 18 of the outer lead body 12 has a connective device operativelyassociated therewith for cooperating with a complimentary structure onthe proximal end portion of the inner lead body 14. More particularly,the proximal end portion 18 of the outer lead body 12 has a helicalthread 26 formed on an exterior surface thereof, spaced from or formedintegral with the proximal electrode 24.

[0038] Referring to FIGS. 2 and 3c-3 d, the inner lead body 14 hasopposed distal and proximal end portions 36 and 38 and an interior lumen40 for accommodating a stylet (not shown) to guide placement of the leadin the great cardiac vein. The inner lead body 14 has a distal electrode42 operatively associated with the distal end portion 36 and a proximalelectrode 44 operatively associated with the proximal end portion 38.The distal electrode 42 is in the form of a ring electrode, as is theproximal electrode 44. However, other types of electrode configurationscan be employed for purposes other than sensing and/or pacing as will bedescribed in more detail hereinbelow. Proximal electrode 44, forexample, can be configured as a connector pin with an axial bore foraccommodating passage of a stylet. The proximal and distal electrodes42, 44 of the inner lead body are electrically connected to one anotherby a conductor such as a monofiliar or multifiliar coil 43, and theyserve as the cathode for coronary sinus lead 10. The proximal endportion 38 of the outer lead body 14 has a connective device in the formof an end cap 46 with an interior helical thread 48 for cooperating withthe helical thread 26 associated with the proximal end portion 18 ofouter lead body 12.

[0039] It is envisioned that the conductor coils 23, 43 used to connectthe respective distal and proximal electrodes of the inner and outerlead bodies could be formed from an insulated wire. The wire could be alow resistance wire such as, for example, MP35N or DFT wire, and theinsulative coating could be PTFE, polyamide, silicone or a similarmaterial.

[0040] Those skilled in the art will readily appreciate that alternativemechanisms may be employed to interconnect the proximal ends of theouter and inner lead bodies 12, 14 without departing from the spirit orscope of the subject disclosure. Moreover, the illustrated threadedconnective mechanism, which is referred to in the art as an IS-1 typeconnector, is merely an example of a connector that may be employed withthe inner and outer lead bodies 12, 14.

[0041] As illustrated in FIG. 4, the inner lead body is dimensioned andconfigured for accommodation within the interior lumen 20 of the outerlead body in such a manner so that the distal end portion 36 of theinner lead body 14 extends from the distal end portion 16 of the outerlead body 12. In particular, the length of the outer lead body 12 isabout between 50 and 80 cm, and the length of the inner lead body 14 isabout between 60 and 100 cm. Thus, the distal end portion 36 of theinner lead body 14 extends from the interior lumen 20 of the outer leadbody about between 10 and 20 cm. The outer diameter of the outer leadbody 12 is about between 6 and 9 F, and the outer diameter of the innerlead body 14 is about between 3 and 5 F. Those skilled in the art willreadily appreciate that the dimensions disclosed herein could varywithout departing from the scope of the invention.

[0042] Referring now to FIG. 5, there is illustrated another coronarysinus lead constructed in accordance with a preferred embodiment of thesubject invention and designated generally by reference numeral 100.Coronary sinus lead 100 is similar to coronary sinus lead 10 in that itis configured for left ventricular pacing and sensing. Lead 100 differshowever in that the outer lead body 112 includes a distal groundelectrode 122 and the inner lead body 114 includes a distal tipelectrode 142.

[0043]FIG. 6 illustrates another coronary sinus lead constructed inaccordance with a preferred embodiment of the subject invention anddesignated generally by reference numeral 200. Coronary sinus lead 200is configured for left ventricular pacing and sensing, and for rightventricular defibrillation. More particularly, the inner lead body 214includes a distal tip electrode 242 (in conjunction with proximal ringelectrode 244) for pacing and/or sensing, and the outer lead body 212includes an elongated distal ground electrode or coil 222 forfacilitating right ventricular defibrillation in conjunction with asecond cardiac lead which will be discussed in greater detainhereinbelow with reference to FIG. 14.

[0044]FIG. 7 illustrates yet another coronary sinus lead constructed inaccordance with a preferred embodiment of the subject invention anddesignated generally by reference numeral 300. Coronary sinus lead 300is configured for left ventricular pacing and sensing, and for rightatrial pacing and sensing. More particularly, the inner lead body 314has a distal tip electrode 342 for pacing and/or sensing, and the outerlead body 312 includes distal ring electrode 322 a for right atrialpacing/sensing and an elongated distal ground electrode 322 b forfacilitating right ventricular defibrillation in conjunction with asecond cardiac lead which will be discussed in greater detainhereinbelow with reference to FIG. 15. In this embodiment, proximal ringelectrode 344 is provided on inner lead body 314 and proximal ground anright atrial electrodes 324 a and 324 b are associated with outer leadbody 312.

[0045] The tip, ring and ground electrodes employed on the inner andouter lead bodies are preferably formed from a platinum/iridium alloy,as is the coiled shock electrode. The inner and outer lead bodies arepreferably formed from silicon, polyurethane, PTFE or a similarbio-compatible insulative plastic or elastomer.

[0046] In accordance with an embodiment of the subject invention, thecoronary sinus lead includes a fixation member operatively associatedwith the distal end portion of the inner lead body. The fixation memberis adapted and configured to anchor the lead within the coronary sinusagainst the flow of blood and the cardiac pressure of the beating heart.Preferably, the fixation member has a polymeric coating containing amedicament that is released into the vascular tissue over time. Thepolymeric coating is preferably absorbable, and the medicament ispreferably a steroid or a similar therapeutic drug for treating thecardiac tissue surrounding the distal end of the lead. Non-polymericcoating s may also be used to carry a medicament for absorption. It isalso envisioned that the fixation member can be electrically active soas to function as a distal electrode for pacing and/or sensing.

[0047] Referring to FIGS. 10a-10 b, one embodiment of the fixationmember is designated generally by reference numeral 50. Fixation member50 includes a pair of radially expandable arms 52 a and 52 b whichextend from an annular base structure 54. The arms 52 a, 52 b are formedfrom a bio-compatible material, such as stainless steel, or a shapememory metal such as a nickel-titanium alloy. Fixation member 50 isoperatively associated with the distal end portion 36 of the inner leadbody and is mounted for movement between a retracted position (FIG. 10a)wherein arms 52 a, 52 b are disposed within the interior lumen 40 ofinner lead body 14 and an extended position (FIG. 10b) wherein arms 52a, 52 b extend radially outwardly to anchor lead body 14 againstlongitudinal displacement. In use, fixation member 50 may be deployedfrom the retracted position to the extended position by extending anelongated stylet or similar structure through the interior lumen 40 ofinner lead body 14. It is envisioned that the distal end of lumen 40would be adapted to limit the movement of the base structure 54 beyond acertain point to maintain it within the interior lumen.

[0048] Referring to FIGS. 11a-11 b, another embodiment of the fixationmember is designated generally by reference numeral 60. Fixation member60 is defined by a radially expandable vascular stent formed from abio-compatible polymeric material or metal that may be braided or cutfrom a tubular structure. It is envisioned that the stent would movefrom a contracted position to a radially expanded position when exposedto body temperature, or in response to retracting a sheath (not shown)initially disposed about the stent during its placement within a bloodvessel.

[0049]FIGS. 12 and 13 illustrate two other embodiments of a fixationmember including a radially expandable cylindrical coil 70 and aradially expandable wire cage 80. These fixation devices may beconstructed and deployed in a manner similar to fixation member 60. Itis envisioned that the distal end portion 16 of the outer lead body 12may also include a fixation member in the form of any one of thepreviously described fixation structures or at least one flexible tineas is known in the art. The fixation member associated with the distalend portion of the outer lead body 12 could be electrically activeand/or provided with a coating containing a medicament.

[0050] Referring now to FIGS. 1, 5, 8 and 9, by way of example, coronarysinus lead 10 is deployed in the following manner for facilitating leftventricular pacing and/or sensing. Initially, as illustrated in FIG. 8,with the assistance of a guiding stylet or catheter (not shown), theouter lead body 12 is extended into the right atrium of the heartthrough the superior vena cava to a position adjacent to theauriculo-ventricular opening to the coronary sinus. At such time, thedistal tip of the outer lead body 12 is in a closed or sealed condition.In this position, the distal ground electrode 22 (anode) of the outerlead body 12 is disposed within the right atrium. Thereafter, asillustrated in FIG. 9, the inner lead body 14 is introduced into thecoronary sinus by way of the interior lumen 20 of the outer lead body12. In essence, the outer lead body 12 serves as a guide catheter tofacilitate the placement of the inner lead body 14 into the coronarysinus and subsequent introduction into the great cardiac vein or branchvein.

[0051] The inner lead body 14 is advanced into the great cardiac vein orbranch vein to a location where the distal tip electrode 42 (cathode) ispositioned so as to be in contact with the wall of the left ventricle,as best seen in FIG. 1. Then, as shown for example in FIG. 4, theproximal end portions 18, 38 of the outer and inner lead bodies 12, 14are threadably connected to one another so as to form an integralstructure. At such a time, either one of the fixation devices 50, 60, 70or 80 may be deployed from the distal end portion 36 of the inner leadbody 14 to prevent longitudinal displacement of lead 10. Furthermore, asimilar fixation structure operatively associated with the distal endportion 16 of the outer lead body 12 may be deployed within the rightatrium to maintain the position of lead 10. Once lead 10 has been fullydeployed and the two lead bodies 12, 14 have been threadably connectedto one another, the lead 10 is operatively connected to a cardiacpacemaker so that it may be employed for left ventricular pacing and/orsensing.

[0052] Referring now to FIG. 14 in conjunction with FIG. 6, coronarysinus lead 200 is employed to facilitate left ventricular pacing and/orsensing in conjunction with a second lead 250 configured for rightventricular pacing and sensing, as well as defibrillation. Moreparticularly, lead 200 is deployed in the manner described above withrespect to lead 10. Lead 250 is extended into the right ventricle by wayof the superior vena cava and is secured therein by a conventionalfixation structure, such as, for example, a helical fixation screw. Asillustrated, lead 250 includes a distal tip electrode 252 for pacingand/or sensing and a distal shock electrode 254 for right ventriculardefibrillation. The ground for defibrillation is supplied by theelongated proximal electrode 224 of the outer lead body 212.

[0053] Referring to FIG. 15 in conjunction with FIG. 7, coronary sinuslead 300 is employed to facilitate left ventricular and right atrialpacing and sensing, in conjunction with a second lead configured forright ventricular pacing and sensing, as well as defibrillation. Moreparticularly, lead 300, which is deployed in the manner described abovewith respect to lead 10 to facilitate left ventricular pacing and/orsensing, right atrial pacing and/or sensing, and right ventriculardefibrillation. As in the previous deployment shown in FIG. 14, lead 250is extended into the right ventricle by way of the superior vena cavaand includes a distal tip electrode 252 for pacing and/or sensing and adistal shock electrode 254 for right ventricular defibrillation inconjunction with the proximal ground electrode 322 b of outer lead body312.

[0054] Referring now to FIG. 16, there is illustrated another embodimentof the coronary sinus lead of the subject invention designated generallyby reference numeral 400. In this embodiment, the distal end portion ofthe outer lead body includes a sensor 445 for monitoring blood flowparameters. The blood flow sensor 445 can take the form of an ultrasonicpulse Doppler sensor, transit-time sensor or a similar sensor. Suchsensors are known in the art as disclosed for example in U.S. Pat. No.5,409,009 to Olson, the disclosure of which is herein incorporated byreference in its entirety.

[0055] Although the coronary sinus lead and placement method of thesubject invention has been described with respect to preferredembodiments, those skilled in the art will readily appreciate thatchanges and modifications may be made thereto without departing from thespirit and scope of the present invention as defined by the appendedclaims.

What is claimed is:
 1. A cardiac lead comprising: a) a first elongatedlead body having opposed proximal and distal end portions and having aninterior lumen extending therethrough, the first lead body includingmeans operatively associated with the distal end portion thereof formeasuring blood flow parameters to facilitate placement of the distalend portion of the first lead body adjacent the coronary sinus, andhaving at least one distal electrode operatively associated with thedistal end portion thereof and a proximal electrode operativelyassociated with the proximal end portion thereof; and b) a secondelongated lead body having opposed proximal and distal end portions, thesecond lead body having at least one distal electrode operativelyassociated with the distal end portion thereof and a proximal electrodeoperatively associated with the proximal end portion thereof, whereinthe second elongated lead body is dimensioned and configured foraccommodation within the interior lumen of the first lead body.
 2. Acardiac lead as recited in claim 1, wherein the means operativelyassociated with the distal end portion of the first lead body formeasuring blood flow parameters is defined by a blood flow sensor.
 3. Acardiac lead as recited in claim 1, wherein the second lead body has alength that is greater than the length of the first lead body.
 4. Acardiac lead as recited in claim 1, wherein a conductor extends throughthe first lead body to connect the distal electrode and the proximalelectrode.
 5. A cardiac lead as recited in claim 1, wherein a conductorextends through the second lead body to connect the distal electrode andthe proximal electrode.
 6. A cardiac lead as recited in claim 1, whereinthe second lead body has an interior lumen extending therethrough.
 7. Acardiac lead as recited in claim 1, wherein the distal electrode of thefirst lead body is a ring electrode.
 8. A cardiac lead as recited inclaim 1, wherein the distal electrode of the first lead body is a coilelectrode.
 9. A cardiac lead as recited in claim 1, wherein the distalelectrode of the first lead body is a ground electrode.
 10. A cardiaclead as recited in claim 1, wherein the distal electrode of the secondlead body is a ring electrode.
 11. A cardiac lead as recited in claim 1,wherein the distal electrode of the second lead body is a tip electrode.12. A cardiac lead as recited in claim 1, wherein the distal electrodeof the first lead body is anodic, and the distal electrode of the secondlead body is cathodic.
 13. A cardiac lead as recited in claim 1, whereinthe proximal electrode of the second lead body is a pin connector.
 14. Acardiac lead as recited in claim 1, wherein the first lead body includesseal means for sealing the interior lumen of the first lead body duringinsertion of the first lead body through the coronary venous system. 15.A cardiac lead as recited in claim 1, wherein the proximal end portionof the first lead body and the proximal end portion of the second leadbody include means for connecting the first lead body to the second leadbody.
 16. A cardiac lead as recited in claim 15, wherein the means forconnecting the first lead body to the second lead body includes athreaded connector.
 17. A cardiac lead comprising: a) a first elongatedlead body having opposed proximal and distal end portions and having aninterior lumen extending therethrough, the first lead body having asensor operatively associated with the distal end portion thereof formeasuring blood flow parameters to facilitate placement of the distalend portion of the first lead body adjacent the coronary sinus, andhaving at least one distal electrode operatively associated with thedistal end portion thereof and a proximal electrode operativelyassociated with the proximal end portion thereof; and b) a secondelongated lead body having opposed proximal and distal end portions, thesecond lead body having at least one distal electrode operativelyassociated with the distal end portion thereof and a proximal electrodeoperatively associated with the proximal end portion thereof, whereinthe second elongated lead body is dimensioned and configured foraccommodation within the interior lumen of the first lead body.